Method for preparing a plastic surface for printing with toner

ABSTRACT

A method for preparing a plastic surface for printing with a toner comprising: forming a layer of an aqueous mixture comprising a first material and a second material on the surface, wherein the first material has an affinity for the plastic and the second material has an affinity for the first material and the toner, and drying the layer.

RELATED APPLICATIONS

The present application is a U.S. national application ofPCT/IL00/00084, filed Feb. 10, 2000.

The invention relates to printing on plastic and in particular topromotion of adhesion of printing inks to a plastic surface.

BACKGROUND

Surfaces of plastic products of all types) such as for example plasticshopping bags, place mats, and decals are printed for purposes ofadvertisement and decoration. However, there are many plastics to whichcommon printing inks do not readily adhere. Often a plastic surface thatis to be printed must be treated prior to printing so that inks that areused to print the su adhere properly to the surface. The treatmentgenerally comprises coating the surface with a primer material that hasa high affinity for both the plastic surface and the inks used to printthe surface. The affinities of the primer for both the plastic and theink bonds ink applied to the primer coated surface to the surface.Typically, the primer comprises or is mixed with volatile organiccompounds potentially dangerous to human health that are released intothe atmosphere during application of the primer to the surface. In orderto protect people present in work areas where the primer is being usedfrom exposure to the compounds, substantial resources have to beinvested to properly ventilate the work areas and to monitorconcentrations of the compounds in the air in the work areas.

SUMMARY OF THE INVENTION

An aspect of some preferred embodiments of the present invention relatesto providing a primer, hereinafter referred to as a “pollution freeprimer”, for bonding a toner ink to a plastic surface that does notrelease organic compounds into the air.

An aspect of some preferred embodiments of the present invention relatesto providing a pollution free primer that adheres with appropriateforces to the plastic surface and the toner so that the toner can beapplied to the surface using an offset process.

An aspect of some preferred embodiments of the present invention relatesto providing a primer that when applied to the plastic surface flows andwets the surface to provide a substantially uniform coating on thesurface.

In a preferred embodiment of the present invention the primer comprisesan aqueous solution of a first material having a strong affinity for theplastic surface mixed with a second material having a strong affinityfor the first material and the toner. The affinities of the primercomponents for each other and for the plastic and the toner are suchthat the toner is efficiently transferred to the plastic from a blanketused in an offset printing process. Preferably the first and secondmaterials form relatively strong bonds to each other at least whendried. Hereinafter, the first material is referred to as a “plasticbonding-agent” and the second material is referred to as a “tonerbonding-agent”.

In a preferred embodiment of the present invention, the plasticbonding-agent is polyethylenimine (PEI) and the toner bonding-agent is adispersed phase of MP4990, which is an aqueous dispersion of copolymerof polyethylene and acrylic acid, manufactured by Michelman. Preferably,the primer is mixed with a surfactant that enhances wetting of theplastic surface by the primer and promotes formation of a uniformcoating of the primer on the plastic surface.

The inventors have found that a thin substantially uniform coating ofthe primer can be applied to a side of a sheet or web of plastic using agravure printing process. The primer adheres well to the plastic and theprimer coated surface can be printed with liquid toners, such as forexample those described in U.S. Pat. No. 5,407,771 to Landa et al., thedisclosure of which is incorporated herein by reference. Preferably, thetoners are ElectroInk® produced and sold by Indigo N. V. of theNetherlands such as ElectroInk® EI-Mark 3.0 and EI-Mark 3.1. Othertoners can be used.

There is therefore provided in accordance with a referred embodiment ofthe present invention a method for preparing a plastic surface forprinting with a toner comprising: forming a layer of an aqueous mixturecomprising a first material and a second material on the surface,wherein the first material has an affinity for the plastic and thesecond material has an affinity for the first material and the toner;and drying the layer.

Preferably, the first material is polyethylenimine. Preferably, thesecond material is a material chosen from the group of materialscomprising: polyethylene acrylic acid copolymer, styrene acrylatecopolymer and styrene-butadiene. Peferably, the weight of the firstmaterial plus the weight of the second material is between about 2% andabout 10% of the weight of the mixture.

Additionally or alternatively, the ratio of the weight of the secondmaterial to the weight of first material in the mixture is between 1 and5. In some preferred embodiments of the present invention, the ratio ofthe weight of the second material to the weight of the first material inthe mixture is substantially equal to 1. In some preferred embodimentsof the present invention, the ratio of the weight of the second materialto the weight of the first material in the mixture is substantiallyequal to 2. In some preferred embodiments of the present invention, theratio of the weight of the second material to the weight of the fistmaterial in the mixture is substantially equal to 3.

In some preferred embodiments of the present invention, the secondmaterial is polyethylene acrylic acid copolymer. In some preferredembodiments of the present invention, the second material is styreneacrylate copolymer. In some preferred embodiments of the presentinvention, the second material is styrene-butadiene.

According to some preferred embodiments of the present invention, themethod comprises adding a surfactant to the mixture. Preferably, thesurfactant is chosen from the group of materials comprising:2,4,7,9-tetramethyl-5-decyn-4, 7-diol; 2,4,7,9-tetramethyl-5-decyn-4,7-diol+3.5 moles ethylene oxide; and sodium dodecyl sulfate.

In some preferred embodiments of the present invention, the surfactantis 2,4,7,9-tetramethyl-5-decyn-4, 7-diol. In some preferred embodimentsof the present invention, the: surfactant is2,4,7,9-tetramethyl-5-decyn-4, 7-diol+3.5 moles ethylene oxide.Additionally or alternatively, after addition of the surfactant, themixture comprises between 1% and 1.5% by weight surfactant.

In some preferred embodiments of the present invention, the surfactantis sodium dodecyl sulfate. Preferably, after addition of the surfactant,the mixture comprises between 2% and 2.5% by weight surfactant.

In some preferred embodiments of the present invention, the firstmaterial is dissolved in water. Preferably, the solution of the firstmaterial comprises between 2% and 10%/ by, weight of the first material.

In some prefer embodiments of the present invention, the second materialis dispersed in water. Preferably, the aqueous dispersion of the secondmaterial comprises between 2% and 10% by weight of the second material.

In some preferred embodiments of the present invention, forming thelayer comprises preparing the mixture in accordance with a procedurecomprising: preparing an aqueous solution of the first material;preparing an aqueous dispersion of the second material; and mixingtogether the aqueous solution and the aqueous dispersion to prepare themixture.

In some preferred embodiments of the present invention, forming a layercomprises forming a layer of an aqueous mixture that does not releaseorganic compounds into the air during drying thereof.

In some preferred embodiments of the present invention, forming a layercomprises forming a layer having a weight per square meter of plasticbetween 0.10 and 0.20 grams after the layer is dry. In some preferredembodiments of the present invention, forming a layer comprises forminga layer having a weight per square meter of plastic between 0.125 and0.175 grams after the layer is dry. In some preferred embodiments of thepresent invention, forming a layer comprises forming a layer having aweight per square meter of plastic between 0.135 and 0.165 grams afterthe layer is dry. In some preferred embodiments of the presentinvention, forming a layer comprises forming a layer having a weight persquare meter of plastic substantially equal to 0.15 grams after thelayer is dry.

In some preferred embodiments of the present invention, forming a layerof the mixture on the surface comprises applying the mixture to thesurface using a gravure roller.

In some preferred embodiments of the present invention forming a layerof the mixture on the surface comprises applying the mixture to thesurface using a gravure roller.

BRIEF DESCRIPTION OF FIGURES

The invention will be more clearly understood from the followingdescription of preferred embodiments thereof read with reference tofigures attached hereto. In the figures, identical structures, elementsor parts that appear in more than one figure are generally labeled withthe same numeral in all the figures in which they appear. Dimensions ofcomponents and features shown in the figures are chosen for convenienceand clarity of presentation and are not necessarily shown to scale. Thefigures are listed below.

FIG. 1 schematically shows preparation of a primer, in accordance with apreferred embodiment of the present invention; and

FIG. 2 schematically shows a method of printing on plastic using aprimer in accordance with a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates preparation of a quantity of primer 20by mixing an aqueous solution 22 of a water-soluble plasticbonding-agent with an aqueous dispersion 24 of an toner bonding-agent,in accordance with a preferred embodiment of the present invention.Preferably, the plastic bonding-agent is polyethylenimine. Preferably,solution 22 is 6%±4% (i.e. from 2% to 10%) by weight ofpolyethylenimine.

In some preferred embodiments of the present invention, the tonerbonding-agent is dispersed phase of MP4990 and the amount by weight ofdispersed phase of MP4990 in aqueous dispersion 24 is preferably aboutthe same as the amount by weight of polyethylenimine in solution 22.Preferably polyethylenimine solution 22 and “MP4990 dispersion 24” aremixed together in equal quantities by weight. However, a quantity ofMP4990 dispersion 24 may be mixed with a quantity of polyethyleniminesolution 22 so that the ratio by weight of dispersed phase of MP4990 topolyethylenimine in primer 20, in accordance with a preferred embodimentof the present invention, has any value in a range from 1 to 5. Thelarge mixing range is possible because dispersed phase of MP4990 has anaffinity of its own to plastic.

Other toner bonding-agents usable to prepare primer 20, in accordancewith a preferred embodiment of the present invention, are a dispersedphase of Styrofan, Acronal 866 or Styronal D808. Styrofan and Styronalare trade names for aqueous polymer dispersions based onstyrene-butadiene sold by BASF. Acronal is a trade name for acrylatehomopolymers and copolymers in dispersed form sold by BASF. For thesematerials, aqueous dispersion 24 is by weight, preferably, 8%±4% of adispersed phase of Styrofan, Acronal 866 or Styronal D808. As in thecase for dispersion 24 formed with MP4990, dispersion 24 formed withStyrofan, Acronal and Styronal is preferably mixed with 6%polyethylenimine solution 22 in equal parts by weight of dispersion 24to solution 22 to form primer 20. A quantity of dispersion 24 based onStyrofan, Acronal or Styronal may be mixed with a quantity ofpolyethylenimine solution 22 to provide a primer 20 in which the ratioof dispersed phase of Styrofan, Acronal or Styronal to polyethyleniminein the primer has a range between 1 and 5, in accordance with apreferred embodiment of the present invention.

In some preferred embodiments of the present invention, a surfactant 26is added to primer 20. In some preferred embodiments of the presentinvention, the surfactant is a solute in Surfynol 104E, which is anaqueous solution of 2,4,7,9-tetramethyl-5-decyn-4, 7-diol, mfg. by AirProducts Inc. Surfynol 104E is added to primer 20 so that preferably,after addition, the primer comprises between 1%-1.5% by weight of thesolute in Surfynol 104E″ (i.e. 2,4,7,9-tetramethyl-5-decyn-4, 7-diol).In some preferred embodiments of the present invention the surfactant isa solute in Surfynol 440, which is the solute in Surfynol 104+3.5 molesEthylene oxide, mfg. By Air Products Inc. Surfynol 440 is added toprimer 20 so that preferably, after addition, the primer comprises byweight about 1% to 1.5% of the solute in Surfynol 440. In some preferredembodiments of the present invention the surfactant is sodium dodecylsulfate which is added to primer 20 so that after addition the primercomprises by weight about 2% to 2.5% surfactant In the case of additionof a surfactant, preferably the amount by weight of polyethylenimineplus dispersed phase of MP4990, Styrofan, Acronal or Styronal in primer20 is between 2% and 10%.

It should be noted that the above method for preparing a primer inaccordance with a preferred embodiment of the present invention is givenby way of example. Other methods known in the art for combiningmaterials to prepare the primer may be used. For example, the primer canbe formed by preparing an aqueous solution of a suitable plasticbonding-agent and dispersing a suitable toner bonding-agent in thesolution or preparing an aqueous dispersion of the toner bonding-agentand dissolving the plastic bonding-agent in the dispersion.

FIG. 2 schematically illustrates printing a plastic web 30 using primer20, in accordance with a preferred embodiment of the present invention.Web 30 is fed from a roll 32 in a direction indicated by arrows 33 sothat it preferably passes between a nip 34 of a rotating gravurecylinder 36 and a backing cylinder 38. Web 30 may be formed for examplefrom bi-axial oriented polypropylene. Preferably, a corona treated side40 of web 30 contacts gravure cylinder 36.

Primer 20 is applied to gravure cylinder 36 from an appropriatedispenser 42 using methods known in the art. Primer 20 that is appliedto gravure cylinder 36 is schematically shown as a layer 44 of primer 20on a region of the surface of gravure cylinder 36. As web 30 passesthrough nip 34, gravure cylinder 36 rotates and transfers primer 20 fromlayer 44 on its surface to web 30 to coat the web with a layer 46 ofprimer 20. Preferably, after drying the weight of layer 46 is about0.15±0.015 grams to each square meter of the surface of web 30. Afterpassing through nip 34 and being coated with primer 20, web 30 passesthrough a drying station, represented by a rectangle 48, at which layer46 of primer 20 is dried. By the time that layer 46 is dry, the plasticbonding-agent, (e.g. polyethylenimine), and the toner bonding-agent inthe primer are bonded together. Web 30 then proceeds to a printer,represented by a rectangle 50, such as an Omnius printer, (mfg. ByIndigo) where the primer coated surface 40 of web 30 is printed with adesired image. Preferably, web 30 is printed with liquid toner, such asfor example, toners produced and sold by Indigo N. V. of the Netherlandsunder the trade names EI-Mark 3.0 and EI-Mark 3.1.

A liquid toner useful for practicing the present invention can beproduced according to the process described below.

Ten parts, by weight, of Elvax II5950 (Mfg. By Du Pont) and five partsby weight of Isopar L (mfg. By Exxon) are mixed for one hour at lowspeed in a jacketed double planetary mixer connected to an oil heatingunit set at 130° C. An additional five part by weight of Isopar L areadded to the mixture in the planetary mixer and after adding theadditional Isopar L, the mixture is mixed at high speed for anadditional hour. Ten parts by weight of Isopar L, preheated to 110° C.are then added and mixing is continued for an hour. The heating unit isthen turned off and mixing is continued until the temperature of themixture in the planetary mixer drops to about 40° C.

Ninety grams of the cooled mixture is transferred to a Union Process 01attritor together with 7.5 g of Mogul L carbon black (sold by Cabot) and120 g of Isopar L. The mixture thus formed is ground using {fraction(3/16)}″ stainless steel media for 24 hours with water cooling, at about20° C. to form a toner concentrate.

The toner concentrate is diluted in Isopar L to a non-volatile solidscontent 1.5%. For each gram of toner solids, 5-100 mg of charge directorsolution is added to form the liquid toner.

Whereas in FIG. 2 a plastic web is shown being coated with a primer andprinted, plastic sheets and surfaces of plastic products can also becoated with primer and printed with toner inks in accordance with apreferred embodiment of the present invention. Also, whereas in FIG. 2the primer is shown being applied to the web using a gravure cylinder,primer may be applied to a suitable plastic surface using other methodsknown in the art, such as for example by spraying or wire coating.Furthermore, application and drying of primer, in accordance with apreferred embodiment of the present invention, does not have to be done“in line” during a printing process as shown in FIG. 2. Primer can beapplied to a surface of a plastic web, sheet or other suitable plasticproduct at a fist site and at a first time and the surface can beprinted at a second site at a second time. For example, after beingcoated with primer, the plastic web, sheet or product can be stored andprinted later. In addition, in accordance with a preferred embodiment ofthe present invention, the primer is useable with plastics other thanbi-axial oriented polypropylene.

In developing pollution free primers suitable for bonding toner inks toplastic, in accordance with preferred embodiments of the presentinvention, the inventors developed water-based primers comprisingdifferent materials and combinations of materials. Each of the primerswas tested to determine its suitability for use in printing on plasticby applying the primer to the corona treated side of a web of bi-axialoriented polypropylene. The primer was applied to the web to a coatweight of 0.15 g/m² using a gravure roller. The web was then printedwith liquid toner ink EI-3.1 using an Omnius printer. The primer wastested for adherence to the surface of the web, uniformity of the primercoating formed on the web and how well toner transferred from a blanketin the printer to the primer and fixed on the web. The primers developedand tested do not release volatile organic materials. Examples of theprimers and results of testing the primers, including those primersdescribed in the discussion of FIG. 1, are presented and discussed inthe following paragraphs.

EXAMPLE 1

A primer was prepared that comprised a 20% by weight aqueous solution ofn-propanol in which dispersed phase of MP4990 was dispersed to aconcentration of 12% by weight The primer coating formed on the web wasuniform and did not evidence patterning. However, adhesion of the primerto the web was poor as determined by a peel test. Transfer of ink fromthe blanket to the primer was unsuccessful and the primer detached fromthe web and adhered to the blanket.

EXAMPLE 2

Another primer comprised a 6% aqueous solution by weight ofpolyethylenimine mixed with an equal amount by weight, of a 6% aqueousdispersion of dispersed phase of MP4990. The mixture was stable anddidn't exhibit phase separation. The primer adhered well to the web,however, it evidenced patterning due to relatively poor wetting of theweb by the primer. Ink transfer and fixing were satisfactory.

EXAMPLE 3

A primer was prepared by forming a mixture comprising a 6% aqueoussolution by weight of polyethylenimine mixed with an equal amount byweight of a 6% aqueous dispersion of dispersed phase of MP4990 (ie. theprimer of Example 2) and adding to the mixture Surfynol 104E as asurfactant. The Surfynol was added to the mixture so that after additionthe mixture was about 1% by weight solute from Surfynol 104E. Adhesionof the primer to the web was excellent and the primer formed asubstantially uniform “un-patterned” coating on the web. Tonertransferred to the primer successfully and fixing was satisfactory.

EXAMPLE 4

A primer similar to the primer of Example 3 was prepared in whichSurfynol 440 was used as a surfactant added to a mixture comprisingequal amounts by weight of a 6% aqueous solution of polyethylenimine anda 6% aqueous dispersion of dispersed phase of MP4990. Surfynol 440 wasadded to the mixture so that after addition the mixture was between 1%to 1.5% by weight solute from Surfynol 440. Adhesion of the primer tothe web was excellent and the primer formed a substantially uniformcoating on the web. Toner transferred successfully to the primer andfixing was satisfactory.

EXAMPLE 5

Another primer similar to the primer of Example 3 was prepared in whichsodium dodecyl sulfide was used as a surfactant added to a mixturecomprising equal amounts by weight of a 6% aqueous solution ofpolyethylenimine and a 6% aqueous dispersion of dispersed phase ofMP4990. The sodium dodecyl sulfate was added to the mixture so thatafter addition, the mixture was between 2%-2.5% by weight sodium dodecylsulfate. Adhesion of the primer to the web was excellent and the primerformed a substantially uniform coating on the web. Toner transferredsuccessfully to the primer and fixing was satisfactory.

EXAMPLE 6

A primer was prepared by mixing one part by weight of a 6% aqueoussolution of polyethylenimine and three parts by weight of a 6%, byweight, aqueous dispersion of dispersed phase of Styrofan. Adhesion ofthe primer to the web was excellent, however, the primer coatingevidenced patterning due to poor wetting of the web by the primer. Tonertransfer was good and fixing was satisfactory.

EXAMPLE 7

A primer was prepared by mixing equal amounts by weight of a 6% aqueoussolution of polyethylenimine and an aqueous dispersion of 12%, byweight, dispersed phase of Acronal 866. Adhesion of the primer to theweb was excellent however, the primer coating evidenced patterning dueto poor wetting of the web by the primer. Toner transfer was good andfixing was satisfactory.

EXAMPLE 8

Another primer was prepared by mixing equal amounts by weight of a 6%aqueous solution of polyethylenimine and an aqueous dispersion that is12%, by weight, dispersed phase of Styronal D808. Adhesion of the primerto the web was good however, the primer coating evidenced patterning dueto poor wetting of the web by the primer. Toner transfer was good andfixing was satisfactory.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of members, components, elements or parts of thesubject or subjects of the verb.

The present invention has been described using detailed descriptions ofpreferred embodiments thereof that are provided by way of example andare not intended to limit the scope of the invention. The describedpreferred embodiments comprise different features, not all of which arerequired in all embodiments of the invention. Some embodiments of thepresent invention utilize only some of the features or possiblecombinations of the features. Variations of embodiments of the presentinvention that are described and embodiments of the present inventioncomprising different combinations of features noted in the describedembodiments will occur to persons of the art. The scope of the inventionis limited only by the following claims.

What is claimed is:
 1. A method for preparing a plastic surface forprinting with a toner comprising: forming a layer of an aqueous mixturecomprising a first material and a second material and a surfactantselected from the group consisting of 2,4,7,9-tetramethyl-5-decyn-4,7-diol; 2,4,7,9-tetramethyl-5-decyn-4, 7-diol+3.5 moles ethylene oxide;and sodium dodecyl sulfate on the surface, wherein the first materialhas an affinity for the plastic and the second material has an affinityfor the first material and the toner; and drying the layer.
 2. A methodaccording to claim 1 wherein the surfactant is2,4,7,9-tetramethyl-5-decyn-4, 7-diol.
 3. A method according to claim 1wherein the surfactant is 2,4,7,9-tetramethyl-5-decyn-4, 7-diol+2.5moles ethylene oxide.
 4. A method according to claim 2 wherein afteraddition of the surfactant, the mixture comprises between 1% and 1.5% byweight surfactant.
 5. A method according to claim 1 wherein thesurfactant is sodium dodecyl sulfate.
 6. A method according to claim 5wherein after addition of the surfactant, the mixture comprises between2% and 2.5% by weight surfactant.
 7. A method according to claim 1wherein layer has a weight per square meter of the plastic surfacebetween 0.10 and 0.20 grams after the layer is dry.
 8. A methodaccording to claim 7 wherein the layer has a weight per square meter ofplastic between 0.125 and 0.175 grams after the layer is dry.
 9. Amethod according to claim 8 wherein the layer has a weight per squaremeter of plastic between 0.135 and 0.165 grams after the layer is dry.10. A method according to claim 8 wherein the layer has a weight persquare meter of plastic substantially equal to 0.15 grams after thelayer is dry.
 11. A method according to claim 1 wherein the firstmaterial is polyethylenimine.
 12. A method according to claim 11 whereinthe second material is a material selected from the group consisting ofpolyethylene acrylic acid copolymer, styrene acrylate copolymer andstyrene-butadiene.
 13. A method according to claim 12 wherein the weightof the first material plus the weight of the second material is betweenabout 2% and about 10% of the weight of the mixture.
 14. A methodaccording to claim 12 wherein the ratio of the weight of the secondmaterial to the weight of first material in the mixture is between 1 and5.
 15. A method according to claim 12 wherein the ratio of the weight ofthe second material to the weight of the first material in the mixtureis substantially equal to
 1. 16. A method according to claim 12 whereinthe ratio of the weight of the second material to the weight of thefirst material in the mixture is substantially equal to
 2. 17. A methodaccording to claim 12 wherein the ratio of the weight of the secondmaterial to the weight of the first material in the mixture issubstantially equal to
 3. 18. A method according to claim 12 wherein thesecond material is polyethylene acrylic acid copolymer.
 19. A methodaccording to claim 12 wherein the second material is styrene acrylatecopolymer.
 20. A method according to claim 12 wherein the secondmaterial is styrene-butadiene.
 21. A method according to claim 1 whereinthe first material is dissolved in water.
 22. A method according toclaim 21 wherein the aqueous solution of the first material comprisesbetween 2% and 10% by weight of the first material.
 23. A methodaccording to claim 21 wherein the second material is dispersed in water.24. A method according to claim 23 wherein the aqueous dispersion of thesecond material comprises between 2% and 10% by weight of the secondmaterial.
 25. A method according to claim 1 wherein forming the layercomprises preparing the mixture in accordance with a procedurecomprising: preparing an aqueous solution of the first material;preparing an aqueous dispersion of the second material; and mixingtogether the aqueous solution and the aqueous dispersion.
 26. A methodaccording to claim 1 wherein forming the layer comprises forming a layerof an aqueous mixture that does not release organic compounds into theair during drying thereof.
 27. A method according to claim 1 whereinforming the layer of the mixture on the surface comprises applying themixture to the surface using a gravure roller.